"Young Doctors in Love," opening today at area theaters, is probably as funny as it needs to be for all practical, commercial purposes.

I haven't checked up on the latest refinements in the perpetual infidelity and heartache practiced by "General Hospital" and its rivals, but it appears that director Garry Marshall and writers Michael Elias and Rich Eustis found old movies like "The Young Interns" just as useful. Their 95-minute assortment of throwaway gags, running gags and deadpan romances are strung along the plot thread of a fast-moving, crisis-strewn year among a new batch of interns at alarming City Hospital.

Michael McKean, no doubt unrecognizable to TV fans who identify him with greasy Lenny on Marshall's "Laverne & Shirley," achieves a remarkable switch to clean-cut respectability as one-half of the principal love affair. Sean Young, slightly more animated than she was as the replicant in "Blade Runner," is the other half. They are aspiring physicians from opposite ends of the spectrum: McKean's Young Dr. Simon August is an oblivious, brilliant snob from Beverly Hills who intends to become "the greatest surgeon the world has ever known," provided he can overcome a phobia which prevents him from actually cutting anything when he gets a scalpel in his hand. Young's Young Dr. Stephanie Brody is a pretty dunce from rural Vermont who aspires to take over the practice of her revered father. Her sudden seizures are eventually diagnosed as "saxipragia mitosis," a dread internal malady which can only be corrected by an emergency operation, which can only be performed by Dr. August.

A subsidiary, hopeless romance is played out between Patrick Collins as Dr. Rist, a sweet-natured wimp with a head full of New Age platitudes (for the record, Elias and Eustis also wrote the movie adaptation of Cyra McFadden's spoof of Marin County New Agers, "The Serial"), and Hector Elizondo as a gruff, profane gangster's son. When his father (Tito Vandis) is hospitalized with a stroke, Elizondo elects to conceal himself by dressing in drag, a disguise unlikely to deceive people slightly more observant than wistful Dr. Rist.

The filmmakers end up shortchanging a third misalliance, involving Pamela Reed as starchy Head Nurse Sprockett and Taylor Negron as the desperate Young Dr. Phil Burns, whose poverty forces him into drug theft. A shame too, because Reed enhances the reputation for versatility that she's already established on the strength of vivid character performances in "The Long Riders," "Melvin and Howard" and "Eyewitness." Marshall seems to lose track of her at a particularly promising moment--when the strait-laced Sprockett has begun to fall for Burns and decides to let her hair down.

The "Airplane!" company enjoyed the advantage of a better focused plot, unifying the characters as well as the random jokes around a single melodramatic crisis. It also enjoyed a choicer cast. Not that "Young Doctors in Love" is compromised by a bunch of slouches. Perhaps the best reason for patronizing it is to relish the expert humorous work of McKean and Reed, Collins and Elizondo, Dabney Coleman as a sadistic chief of surgery, Harry Dean Stanton and Saul Rubinek as a disreputable team of pathologists, and several other accomplished cast members.

The first feature directed by Marshall after a hugely successful TV comedy career engineering "Happy Days," "Laverne & Shirley" and "Mork and Mindy," "Young Doctors" demonstrates a flair for pictorial gags staged slightly off-center or in the background. There's a neat bit with a nurse dispensing pills while gliding through the wards on a skateboard and a remarkably sustained passage in which Gary Friedkin, as the diminutive Dr. Milt Chamberlain, tries to hang up the receiver of a phone located several feet over his head.

People averse to profane humor should probably avoid "Young Doctors," but it offers a reasonable return on a modest investment in facetiousness.